Cis-2,3 Dimethyl thiirane

The thermal desulfonylation of episulfones is highly stereospecific e.g., cis-2,3-dimethyl-thiirane-1,1-dioxide gives cw-2-butene , and trans- and cw-2,3-diphenyl thiirane 1,1-dioxides give trans and cis stilbenes, respectively . This result is remarkable in that the Woodward-Hoffman symmetry selection rules for inter-molecular cycloadditions (and their reversals) appear to exclude a concerted thermal decomposition of thiirane-l,l-dioxides . ... 

Cis-2,3 dimethyl thiirane (DMT) and cyclohexene sulfide (CS) were studied for this purpose. 

In poly cis 2,3 dimethyl thiirane the peak located at 45.8 ppm (CDCU solvent, reference to IMS) was clearly assigned to the me-thine chain carbon of-diisotactic structure as it was directly increasing with the optical activity of the polymer. Three other peaks corresponding to chain carbons were found, showing that other structures than the simple disyndiotactic one (II) are also present. 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of ds-2,3-dimethyl thiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

In the cationic polymerization of heterocycles, a similar phenomenon was observed by Goethals in the polymerization of propylene sulfide and trans 2,3-dimethyl-thiirane. The latter monomer polymerizes rapidly and quantitatively to a linear polymer which is then relatively slowly converted into 3,4,6,7-tetramethyl-l, 2,5-tri-thiepane (J67a). In this particular process, the macroring formation is a practically irreversible reaction and differs in this sense from the equilibrium processes discussed so far. The irreversibility is due to the formation of one molecule of cis-butene per one molecule of a cyclic trithiepane ... 

Photolysis.—Photochemical transformations of thietan derivatives have not received much attention, but it appears that the initial process is homolysis of a C—S bond, and that extrusion of sulphur is not important, in contrast to the case for thiirans. A reversed [2 + 2]cycloaddition may occur via initial homolysis of the C—S bond, 2,2-diphenyl-3,3-dimethyl-4-isopropylidenethietan, for example, giving l,l-diphenyl-2,2-dimethyl-ethylene, and rra j-2-phenyl-3-benzoylthiiran being converted into a mixture of cis- and /mns-benzalacetophenone, probably by way of its triplet excited state. Thietan vapour on photolysis gave mixtures containing ethylene, propylene, and polymer, and on prolonged irradiation, 2-methylthiiran. ... 

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